Standard automobiles have attached rear view mirrors to assist the driver in checking whether there are obstacles in the rearend of the automobile. However, this conventional apparatus is not sufficient due to its reliability on the accuracy of one's vision and neglects the fact that blind spots exist.
There are various detection systems which are able to enhance the ability of the driver to check whether obstacles are present. Such systems are disclosed in U.S. Pat. No. 4,543,577 to Tachibana, U.S. Pat No. 4,467,313 to Yoshino, and U.S. Pat. No. 5,210,521 to Hojell. These devices help detect moving objects, nearby persons, and the like.
Nevertheless, these devices have many shortcomings due to their dependency on "pulse transmission mode". The pulse is transmitted using mechanical vibration. The remaining or excess vibration can easily enter into a transmitting element and hence the effectiveness of a receptor significantly decreases. In addition, the pulse transmission mode's time is brief and its actual energy that is transmitted is very weak.
Furthermore, there is much ultrasonic distortion in the air such as collision of metals and wind turbulence which may produce strong ultrasound thus making it difficult to distinguish from intended vibrations. Conclusively, "pulse transmission mode" is difficult to operate and has minimal reliability.
Accordingly, there is still a present need for a detection system which is able to notify the driver of objects present whether in motion or not, at a reasonable distance by using "frequency modulation current wave mode".